No abstract

Stereotactic radiosurgery (SRS) with >5 fraction (fr) has been increasingly adopted for brain metastases (BMs), given the current awareness of limited brain tolerance for ≤5 fr. The target volume/configuration change and/or deviation within the cranium during fractionated SRS can be unpredictable and critical uncertainties affecting treatment accuracy, plus the effect of these events on the long-term outcome remains uncertain. Herein, we describe a case of two challenging BMs treated by 10 fr SRS with a unique dose-gradient optimization strategy, in which the large cystic tumor revealed an intriguing correlation of such inter-fractional change with late radiographic sequela, suggesting a dose threshold for attaining longterm local tumor control and being immune to symptomatic brain necrosis.A 63-year-old man presented with two cystic lesions located in the left parietal lobe (19.9 cm 3 ) and pons (1.1 cm 3 ) one month after surgery for esophageal squamous cell carcinoma. The principles for 10 fr SRS were as follows: (1) very inhomogeneous gross tumor volume (GTV) dose covered by 53 Gy, biologically effective dose with an alpha/beta ratio of 10 (BED 10 ) of ≥80 Gy; (2) moderate dose spillage margin outside the GTV boundary: 2-2.5 mm outside the GTV margin was covered by 37 Gy, BED 10 of ≈50 Gy; (3) concentricallylaminated, steep dose increase inside the GTV boundary: 2 mm inside the GTV margin was covered by ≥62 Gy, BED 10 of ≥100 Gy. At the completion of SRS, the parietal lesion showed significant shrinking and dorsomedial shifting with slight evisceration of the GTV, followed by marked regression of the parietal lesion within four months. At 13.5 months, a cystic change was noted at the dorsal part of the remnant. At 16.7 months, ventral enhancement gradually expanded without enlargement of the dorsal cystic component. On the T2-weighted images, the dorsal low-intensity remnant and ventral iso-intensity blurry-demarcated component were contrasting. Pathological examinations during and after lesionectomy at 17.4 months revealed necrosis only. At 30.5 months, the patient had a left visual field defect without recurrence. In contrast, the pons lesion showed no notable change during 10 fr SRS and nearly complete remission over six months with its sustainment without radiation injury at 30.5 months.Taken together, 10 fr SRS with a sufficient BED 10 can provide superior tumor response and safety for BM that is not amenable to ≤5 fr SRS. Although a very inhomogeneous GTV dose can contribute to early and adequate tumor shrinkage and subsequent local tumor eradication, significant tumor shrinkage during fractionated SRS (fSRS) inevitably results in unnecessary higher dose exposure to the surrounding brain, which could lead to late radiation injury requiring intervention. The optimum dose should be determined through further investigation, in consideration of the dynamic and unpredictable nature of the actual absorbed doses to both the tumor and the surrounding brain.

Summary Figure   Working model for the ERBIN–p0071 interaction at cell‐cell adhesions. ERBIN is associated with p0071 at adherens junctions and desmosomes. p0071 is thought to interact with classic cadherins or desmosomal cadherins (Hatzfeld 1999). The subcellular localization of ERBIN may be regulated by the Rho family and other signals controlling cell polarity. Background: ERBIN, an ErbB2 receptor‐interacting protein, belongs to a recently described family of proteins termed the LAP [leucine‐rich repeats and PSD‐95/dLg‐A/ZO‐1 (PDZ) domains] family which has essential roles in establishment of cell polarity. Results: To identify new ERBIN‐binding proteins, we screened a yeast two‐hybrid library, using the carboxyl‐terminal fragment of ERBIN containing PDZ domain as the bait, and we isolated p0071 (also called plakophilin‐4) as an ERBIN‐interacting protein. p0071 is a member of the p120 catenin family, which are defined as proteins with 10 armadillo repeats, and localizes along the cell‐cell border. The ERBIN PDZ domain binds the COOH‐terminus of p0071 containing the PDZ domain‐binding sequence. Endogenous ERBIN was co‐immunoprecipitated with p0071. In fully polarized Madin–Darby canine kidney (MDCK) cells, ERBIN co‐localized largely with β‐catenin and partly with desmoplakin along the lateral plasma membrane domain. At these cell‐cell contact regions, ERBIN co‐localizes with p0071. Over‐expression of the dominant active forms of Cdc42, Rac1 or RhoA, Rho family small GTPases, resulted in a marked accumulation of ERBIN at the cell‐cell contacts of MDCK and HeLa cells. Conclusion: These results show that ERBIN interacts in vivo with p0071 and that it may be involved in the organization of adherens junctions and the desmosomes of epithelia. In addition, we demonstrated that the subcellular localization of ERBIN might be regulated by Rho family small GTPases.